Field of the Invention
The present invention relates to a roll-up apparatus.
Description of the Related Art
A sheet conveyance apparatus for conveying a sheet by a conveyance roller is required to stably perform a roll-up operation when rolling up a roll sheet. In a large-format printing apparatus disclosed in Japanese Patent Laid-Open No. 2012-236305, a roll-up apparatus is arranged on the downstream side of a printhead to roll up a roll sheet fed by a sheet conveyance roller. To convey the long continuous sheet without causing a distortion or wrinkle, a feed roller pair is provided on the upstream side of the print position in the medium conveyance direction, and a tension roller is provided on the downstream side. The tension roller can adjust a tension to be applied to the sheet.
In a medium conveyance mechanism disclosed in Japanese Patent Laid-Open No. 2011-11889, when the roll-up amount of a sheet that is fed from a printer and rolled up around a winding tube increases, the weight and diameter of the winding tube increase, and the value of moment of inertia of the winding tube increases. For this reason, the tension applied to the sheet rolled up around the winding tube largely changes, and the tension applied to the sheet portion progressively fed in the printer largely changes. To reduce the stress on the sheet, when conveying the sheet while applying the tension, the medium conveyance mechanism turns on/off a roll-up motor at a predetermined frequency, thereby adding/releasing the tension to/from the sheet.
In the large-format printing apparatus described in Japanese Patent Laid-Open No. 2012-236305, however, the tension roller serving as a tension application unit is arranged between the print position and a roll-up mechanical unit that rolls up the sheet around a paper tube. In this printing apparatus, the roll-up mechanical unit and the tension application unit are different members. This makes the apparatus arrangement complex and bulky and also increases the manufacturing cost.
In the medium conveyance mechanism described in Japanese Patent Laid-Open No. 2011-11889, the tension is added/released at a predetermined frequency. As the starting point of ON/OFF control of the roll-up motor for this purpose, the detection result of a first detection unit configured to detect the tension difference in the sheet width direction and a second detection unit configured to detect a positional shift in the width direction or a count value at a predetermined time interval or for a predetermined scan count is employed. In the digital control method of turning on/off the motor, the sheet may slack depending on its weight, and roll-up may be unstable. For example, when ON/OFF-controlling the motor in each scan, the slack of the sheet may be amplified. There is also apprehension that the apparatus arrangement may be complicated by providing special detection units such as the first and second detection units.
The present invention provides a technique of performing a stable roll-up operation by a simple arrangement.